Lecture 9

Lecture 9 - Plants. What are they? For more than the first...

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1 Plants. What are they? Figure 29.1 • For more than the first 3 billion years of Earth’s history the terrestrial surface was lifeless • Plants moved onto land at least 475 million years ago – Insects colonized land at roughly the same time Challenges of a terrestrial environment • Desiccation • Support • Transport • Reproduction Green alga called called charophyceans are the closest relatives of land plants Chara globularis - a fresh water charophycean • Comparisons of both nuclear and chloroplast genes find charophyceans are the closest living relatives of land plants • Morphological features that land plants share only with charophyceans: – Rose-shaped complexes for cellulose synthesis – Peroxisome enzymes – Structure of flagellated sperm – Formation of a phragmoplast during cell division 30 nm Figure 29.2 Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Vascular plants Land plants Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Charophyceans Liverworts Hornworts Mosses Lycophytes (club mosses, spike mosses, quilworts) Pterophyte (ferns, horsetails, whisk fern) Gymnosperms Angiosperms 3 Groups Non-vascular plants (Bryophytes) Seedless vascular plants Pterophytes (Ferns) Lycophytes Seed plants Gymnosperms Angiosperms Alternation of generations Terrestrial adaptations
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2 • Non-vascular plants (Bryophytes) LIVERWORTS (PHYLUM HEPATOPHYTA) HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA) Gametophore of female gametophyte Marchantia polymorpha , a “thal oid” liverwort Foot Sporangium Seta 500 µ m Marchantia sporophyte (LM) Plagiochila deltoidea , a “leafy” liverwort An Anthoceros hornwort species Sporophyte Gametophyte Polytrichum commune , hairy-cap moss Sporophyte Gametophyte Figure 29.9 • In all three bryophyte phyla – Gametophytes are larger and longer-living than sporophytes Mature sporophytes Young sporophyte Male gametophyte Raindrop Sperm Key Haploid ( n ) Diploid (2 n ) Antheridia Female gametophyte Egg Archegonia FERTILIZATION (within archegonium) Zygote Archegonium Embryo Female gametophytes Gametophore Foot Capsule (sporangium) Seta Peristome Spores Protonemata “Bud” “Bud” MEIOSIS Sporangium Calyptra Capsule with peristome (LM) Rhizoid Mature sporophytes Spores develop into threadlike protonemata. 1 The haploid protonemata produce “buds” that grow into gametophytes. 2 Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. 3 A sperm swims through a film of moisture to an archegonium and fertilizes the egg. 4
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Lecture 9 - Plants. What are they? For more than the first...

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